Determination of a volume of interest (VOI) (e.g., a tumor site) in a three-dimensional (3D) medical image may help a user (e.g., a doctor, an imaging engineer) analyze the VOI better. The VOI may be segmented based on a seed point determined by the user based on his or her experience. Different seed points selected by the user may cause different results of determination of the VOI, which often renders the determination of the VOI inconsistent and, in some occasions, inaccurate. Therefore, it is desirable to provide systems and methods for image segmentation that can improve the accuracy and the stability of the determination of the VOI in an image.